Treatment of sulfuric acid sludge



United States Patent TREATMENT OF SULFURIC ACID SLUDGE Peter B. Murray,Swarthmore, Pa, assignor to Sun Oil Company, Philadelphia, Pa., acorporation of New Jersey Application June 25, 1956, Serial No. 593,587

6 Claims. (Cl. 23-178) This invention relates to the treatment ofsulfuric acid sludge produced in petroleum refinery operations involvingcontact of hydrocarbons wtih sulfuric acid.

Sulfuric acid sludge produced in petroleum refinery operations presentsa difficult problem with regard to waste disposal, and it is desirableto provide satisfactory ways of obtaining valuable materials from thesludge, rather than discharging the sludge. Hydrogen sulfide produced invarious refinery operations also presents a disposal problem, and it isdesirable to provide satisfactory ways of converting hydrogen sulfideinto elemental sulfur or more valuable sulfur compounds. According tothe invention, the above desirable features are accomplished bycontacting hydrogen sulfide and sulfuric acid sludge under conditions assubsequently specified including the use of temperatures not exceeding250 F. It has been found that the sulfur in both the hydrogen sulfideand the sulfuric acid sludge can be converted in such manner intoelemental sulfur, or into elemental sulfur and sulfur dioxide.

The invention is particularly advantageous as applied to sulfuric acidalkylation sludge, produced in processes involving hydrocarbonalkylation employing sulfuric acid as alkylation catalyst. Variousalkylation processes are well known in the art, for alkylating compoundssuch as isobutane or isopentane with olefinic hydrocarbons such aspropylene, butylene, amylenes, etc. Customary practice involves the useof sulfuric acid having initial con centration of about 99%, theoperation being continued until the concentration of the sulfuric acidhas decreased substantially, for example to a concentration within theapproximate range from 85 to 90 percent. Typical compositions of theused alkylation sludge at this point include a'total carbon content ofto 8%, the sludge comprising mainly H 50 and hydrocarbon sul fonates.

In the prior art, alkylation sludge has been decomposed in the presenceof coke, at a temperature for example of about 1800 F., in order toconvert sulfuric acid to sulfur dioxide and hydrocarbons to coke. Theprocess of the present invention is advantageous in providing conversionof sulfuric acid into sulfur, or into sulfur and sulfur dioxide, whileavoiding the high temperatures and coke-handling problem of prior artoperation.

The temperature of the contacting according to the invention is withinthe approximate range from 40 F. to 250 F., and preferably within theapproximate range from 70 F. to 150 F. Excessively high temperaturesshould not be employed, since they result in charring. Catalysts fordecomposition of H 80 to S0 e. g. mercuric sulfate, can be employed ifdesired.

The highest temperature at which the process according to the inventioncan be carried out without excessive charring of the sludge increaseswith decreasing concentration of H 80, in the sludge. Thus, it ispossible, in operation where the H 80 concentration declines to below75% for example, to increase the temperature correspondingly in order toincrease the rate of conversion of H 80 Preferably, the temperatureswill at all times be within the approximate range from 40 F. to 250 F.,though in some instances it is possible to use temperatures above 250F., and up to 400 F. for example, when the H 80 concentration hasdeclined to a suitably low level.

The process according to the invention is preferably carried out at apressure of about 1 to 30 atmospheres. Elevated pressures favorconversion of H 80 but satisfactory results can be obtained at ordinaryatmospheric pressure.

Elemental sulfur is formed in the process according to the invention bydecomposition of H 80 and the reaction mixture is preferablycontinuously agitated in order to keep the elemental sulfur which isformed suspended in the reaction mixture. Elemental sulfur can berecovered from the reaction mixture, upon completion of the process, inany suitable manner, for example by extraction with a suitable solventsuch as an aromatic hydrocarbon.

At suitable rates of contacting of H 8 with sulfuric acid sludge, forexample 20 to 80 volumes of H 8 at standard conditions per volume ofsludge per hour, the H S supplied to the process is completely convertedinto elemental sulfur and S0 as long as the concentration of sulfuricacid in the sludge is sufiiciently high, for example above about weightpercent. As subsequently shown in connection with Figure 2, the extentof conversion of H 5 when substantially pure aqueous sulfuric acid isemployed, is substantially less than when sulfuric acid sludge isemployed, indicating that there are materials in the sulfuric acidsludge which catalyze the conversion.

SO which is formed in the reaction between H 3 and H may further reactwith H; present in the con version zone, to form elemental sulfur inaddition to that formed in the initial reaction. The two reactions thusinvolved are as follows:

When the sulfuric acid concentration is relatively high in theconversion zone, and the H 8 charged is substantially completelyconsumed in the first reaction, the eflluent gases from the conversionzone contain 80,. The S0 in the effluent gases can be reacted if desiredwith additional H 8 to form additional elemental sulfur. Alternatively,the S0 can be converted to S0 and ultimately to sulfuric acid by knownmethods.

When the sulfuric acid concentration is relatively low, and the H Scharged is not completely consumed in the reaction with H 80 the S0formed is substantially completely converted to elemental sulfur in theconversion Zone by reaction with excess H 5, and the efiuent gases fromthe conversion zone contain H 8 but are substantially free of S0 In suchcases, the eflluent gases containing H 3 are preferably recycled to theconversion zone.

In a preferred embodiment of the invention, the process is performed incontinuous fashion, with the sulfuric acid in the conversion zone beingmaintained at a relatively low concentration, e. g. about 70.weightpercent. In order' to maintain the desired concentration, sulfuric acidsludge having relatively high concentration, e. g. tois introduced intothe conversion zone periodically or continuously, and relatively lowconcentration sludge is withdrawn from the conversion zone eitherperiodically or continuously. The effluent gases contain H S but aresubstantially free of S0 and are recycled to the conversion zone. Suchrecycling of H 8 permits conversion of more of the H 80 contained in thesludge than can be obtained under similar conditions in the absence ofsuch recycling.

The invention can also be carried out according to batch technique,beginning with sludge having concentration of about 85 to 90% forexample. In the early stages of the process, the efiluent gases contain50;, but are substantially free of H 5, whereas in the later stages theefliuent gases contain H 8 but are substantially free of The inventionwill be further described with reference to the attached drawing, inwhich Figure l is a schematic flowsheet illustrating embodiments of theinvention, and Figure 2 is a graph illustrating the process of theinvention as compared with the contacting of H 8 with substantially pureaqueous sulfuric acid.

Referring to Figure 1, sulfuric acid sludge comprising H 50 in 75 to 90%concentration for example, and carbonaceous material is introduced intosludge treating zone 10 through line 11, and is contacted therein with HS introduced through line 12. The contacting is performed in continuousmanner, with sludge having relatively low concentration, e. g. about70%, being Withdrawn, periodically or continuously, through line 13. Thesludge treating zone 10 is preferably equipped with agitating means, inorder to keep elemental sulfur suspended in the sludge. The averageconcentration of the sludge in zone 10 is about 70%, and the effluentgases contain H 8, but are substantially free of S The efiiuent gasesare removed through line 14 and recycled to line 12 through line 15.

The sludge withdrawn through line 13 is introduced through sulfurextraction zone 16, wherein it is contacted with a solvent for sulfurintroduced through lines 17 and 18. The temperature is sufficientlyhigh, e. g. about 200 F., to provide satisfactory solution of sulfur inthe solvent. The solvent phase containing dissolved sulfur is separatedfrom the sludge and introduced through line 19 into sulfur recovery zone20, the sludge being removed through line 21. In zone 20, sulfur isprecipitated from the solution, e. g. by cooling to room temperature,and removed through line 21, the solvent being decanted and recycledthrough line 22.

In another embodiment of the process according to the invention, theprocess can be carried out according to batch technique, the treatedsludge being removed from zone through line 13 only at the end of thecontacting operation, rather than periodically or continuously. In theearly stages of the operation, the concentration of sulfuric acid in thesludge is relatively high, and the efiiuent gases contain S0 but aresubstantially free of H 8. The effluent gases can be removed throughline if desired, or alternatively can be passed through line 32 intotreating zone 33 wherein the sulfur dioxide from the sludge treatingzone and hydrogen sulfide from line 34 are reacted-to form elementalsulfur. This reaction occurs satisfactorily at room temperature, thoughhigher temperatures can be employed if desired. The reaction can beperformed in the presence of water, or according to any of the otherknown processes for reaction of hydrogen sulfide and sulfur dioxide toform elemental sulfur. Eflluent gases if any can be withdrawn throughline 35 and recycled to zone 33 if desired. Sulfur formed at zone 33 iswithdrawn through line 36, and can be subjected to sulfur refiningoperations as well known in the art.

In later stages of operation, when the sulfuric acid content hasdecreased to below 75% for example, the effluent gases from zone 10contain H 8 but substantially no S0 and can be recycled through lines 14and 15, in the manner previously described.

The following example illustrates the invention:

A batch process conforming generally to that described with reference toFigure 1 was carried out, the initial temperature in zone 10 being about85 F., and the temperature rising to about 150 F. during the course ofthe contacting. The sulfuric acid sludge was an alkylation sludgeinitially containing about 89 weight percent of sulfuric acid, andhaving carbon content corresponding to a hydrocarbon sulfonates contentof 11.2 weight percent, assuming such hydrocarbon sulfonates to have theaverage formula C H SO H. cc. of the sludge were employed, weighing174.5 grams. The pressure in the contacting zone 10 was within the rangefrom 250 to 500 mm. of Hg gauge. The vapor hourly space velocity duringthe first 245 minutes was 24 volumes of H 8 per volume of sludge perhour, and the space rate during the next 205 minutes was 40 volumes pervolume per hour. The total contacting time was 8 hours, during which acalculated, 1.2 moles of H 8 were charged. 23 grams of sulfur wererecovered from the sludge in zone 10, and an additional 27 grams ofsulfur were recovered from the treating zone 33 wherein the effluentgases and H 8 were reacted in the presence of water. The total recoveryof 50 grams corresponded to a calculated sulfur yield of 51 grams. Thefinal concentration of the sludge was 75.5 weight percent sulfuric acidand 4.1 weight percent hydrocarbon sulfonates, the remainder beingprimarily water. During the 8 hour period, the H 8 charged wascompletely converted, so that the efliuen gases from zone 10 containedno H 8.

Referring now to Figure 2, results obtained according to the process ofthe invention are shown in comparison with results obtained in similaroperation employingfresh 90% sulfuric acid; both runs were made at F.and vapor hourly space velocity of 36, the conditions being generallysimilar to those described in the preceding example. The percentconversion of H S .is plotted against time, and it is readily seen thatthe substantially pure 90% sulfuric acid provides much poorer conversionof H 8 than the alkylation sludge which is treated according to theprocess of the invention.

Although the invention has been described previously in connection withthe treatment of alkylation sludge, it is to be understood that othersulfuric acid sludges, produced in any of various known processes, canalso be satisfactorily treated according to the invention. 'Thepetroleum refinery processes for treatment of hydrocarbons with sulfuricacid generally produce sludges which contain materials promoting thereaction of H 8 with H 80 under the conditions of the present process.In the process of the invention, elevated temperatures and pressurespermit greater conversion of H 80 while still obtaining S0 in theefiluent gases from the conversion zone. Thus, in a batch process, the H80 concentration at which the effluent gases cease' to contain 80;, maybe about 75% when the conversion zone is at l to 2 atmospheres pressureand the temperature is 40 F. to F. for example, and may be substantiallylower when the conversion zone is at substantially higher pressure ortemperature. And, in a continuous process in which the H 30concentration is maintained at 70%. the effluent gases contain H S butnot S0 if the conversion zone is maintained at l to 2 atmospherespressure and 40 to 150 F. for example, and contain S0 but not H 5 if theconversion zone is maintained at sufficiently higher pressure ortemperature. In the light of the present specification, a person skilledin the art can select proper pressures and H 80 concentrations toproduce the desired results.

In continuous processes, where the efiluent gases contain H 8 but no S0preferred H 50 concentrations are within the approximate range from 50to 75 weight percent. Where the efilulent gases contain S0 but not H 8,preferred H 50 concentrations are within the approximate range from 65to 90 weight percent; at the lower H 80 concentrations within thisrange, relatively high pressures and/or temperatures are needed toprovide the desired effluent gas composition.

The invention claimed is:

1. Process for treating sulfuric acid sludge which coxnv prisescontact-ing sludge produced in sulfuric acid treatment of petroleumhydrocarbons with added hydrogen sulfide at a temperature within theapproximate range from 40 F. to 250 F., thereby forming elementalsulfur, and separating elemental sulfur from the sludge.

2. Process for treating sulfuric acid sludge which com-- prisescontacting sludge produced in sulfuric acid treatment of petroleumhydrocarbons, which sludge has concentration of H 80 within theapproximate range from 50 to 75 weight percent, with added hydrogensulfide in a conversion zone at a temperature within the approximaterange from 40 F. to 250 F., thereby to form elemental sulfur;introducing sludge having sulfuric acid concentration higher than thefirst-named concentration into the conversion zone in order to maintainthe firstnamed concentration; withdrawing sludge from the conversionzone; withdrawing gases containing hydrogen sulfide from the conversionzone; recycling the withdrawn gases to the conversion zone; andseparating elemental sulfur from the sludge.

3. Process for treating sulfuric acid sludge which comprises: contactingsludge produced in sulfuric acid treatment of petroleum hydrocarbons,which sludge has concentration of H 80 within the approximate range from65 to 90 weight percent, with added hydrogen sulfide in a conversionzone at a temperature within the approximate range from 40 F. to 250 F.,thereby to form elemental sulfur; introducing sludge having sulfuricacid concentration which is higher than the first-named concentrationinto the conversion zone in order to maintain the first-namedconcentration; withdrawing sludge from the conversion zone; withdrawinggases containing sulfur dioxide from the conversion zone; and contactingthe withdrawn gases with hydrogen sulfide in a second conversion zone,thereby to form elemental sulfur.

4. Process for treating sulfuric acid sludge which comprises contactingsludge produced in sulfuric acid treatment of petroleum hydrocarbonswith added hydrogen sulfide in a conversion zone at a temperature withinthe approximate range from F. to 250 F.; withdrawing from the conversionzone gases containing sulfur dioxide; continuing the conversion untilthe efiluent gases contain hydrogen sulfide and are substantially freeof sulfur dioxide; recycling such efiluent gases containing hydrogensulfide to the conversion zone; and recovering elemental sulfur from thesludge.

5. Process according to claim 4 wherein said sulfur dioxide is contactedwith additional hydrogen sulfide to form elemental sulfur.

6. Process for treating sulfuric acid sludge which comprises contactingsludge produced in sulfuric acid treatment of petroleum hydrocarbons,which sludge has concentration of H 80 within the approximate range from75 Weight percent to 90 weight percent, with added hydrogen sulfide in'aconversion zone at a temperature within the approximate range from 40 F.to 250 F., thereby to form elemental sulfur and reduce the concentrationof H 80 in the sludge to a concentration within the approximate rangefrom to weight percent; contacting the resulting sludge with hydrogensulfide in a conversion zone at a temperature higher than the firstnamedtemperature, thereby to form elemental sulfur; and separating elementalsulfur from the sludge.

References Cited in the file of this patent UNITED STATES PATENTS1,057,395 Robinson Mar. 25, 1913 1,953,225 Hechenbeikner Apr. 3, 19342,153,337 Oliver Apr. 4, 1939 2,737,450 Morningstar Mar. 6, 1956

1. PROCESS FOR TREATING SULFURIC ACID SLUDGE WHICH COMPRISES CONTACTINGSLUDGE PRODUCED IN SULFURIC ACID TREATMENT OF PETROLEUM HYDROCARBONSWITH ADDED HYDROGEN SULFIDE AT A TEMPERATURE WITHIN THE APPROXIMATERANGE FROM 40*F. TO 250*F., THEREBY FORMING ELEMENTAL SULFUR, ANDSEPARATING ELEMENTAL SULFUR FROM THE SLUDGE.